Method of making a polyimide in a low-boiling solvent

ABSTRACT

A method of making a solution of a polyimide from a diamine monomer and a dianhydride monomer is disclosed. A solution or slurry of one of the monomers in a solvent that boils at a temperature between about 80° C. and about 160° C. is prepared. The solution or slurry is heated to a temperature between about 80° C. and about 160° C. and the other monomer is slowly added to the solution or slurry. Polyamic acid that is formed quickly imidizes to form the polyimide.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims priority to U.S.application Ser. No. 09/676,295, which was filed Sep. 28, 2000 now U.S.Pat. No. 6,451,955.

BACKGROUND OF THE INVENTION

This invention relates to a method of reacting a dianhydride and adiamine in a low-boiling solvent to make a polyimide. In particular, itrelates to preparing a polyimide by slowly adding one of the monomers toa solution of the other monomer in a low-boiling, solvent that is heatedto a temperature sufficient to fully imidize polyamic acid as soon as itis formed.

In chip scale packaging, semiconductor dies are attached to FR4 or BTsubstrates using a solution of a polyimidesiloxane adhesive. Atemperature below 150° C. must be used to protect delicate electroniccomponents. To achieve adhesion below 150° C., the solvent in thesolution of the polyimidesiloxane adhesive must be removable at atemperature below 150° C., which means that solvents such as N-methylpyrrolidinone (NMP), which boils at 202° C., cannot be used.

A polyimidesiloxane is made by reacting a dianhydride with a diamine ina solvent, forming an intermediate polyamic acid. That reaction willoccur at room temperature. The solution of the polyamic acid is thenheated to about 140 to about 150° C. to imidize the polyamic acid. Whilethe intermediate polyamic acid is soluble in polar solvents such as NMP,unfortunately it is not soluble in the low-boiling solvents needed forlow temperature adhesive applications, and a gummy precipitate forms.The polyimidesiloxane could be prepared in a high-boiling solvent, suchas NMP, precipitated in water, washed, dried, and the solidpolyimidesiloxane redissolved in a low-boiling solvent. It would be moreconvenient, less expensive, and less wasteful, however, to prepare thepolyimidesiloxane in the low-boiling solvent and thereby avoid the extraevaporation and redissolving steps.

SUMMARY OF THE INVENTION

We have discovered a way to prepare a solution of a polyimide in alow-boiling solvent. In our invention, a solution or slurry is firstprepared of one of the monomers in the solvent. That solution is heatedto about 80 to about 160° C. and the other monomer is slowly added. Bypreparing the polyimide in this manner, the insoluble polyamic acidintermediate that is formed converts to the soluble polyimide before itcan precipitate. Thus, the polyimide can be prepared in the same solventin which it is to be used and it is not necessary to use one solvent forits preparation and a different solvent for its use.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention is applicable to any polyimide that is soluble in alow-boiling solvent as described herein.

The polyimide can be prepared by reacting an aromatic dianhydride with adiamine. Generally, stoichiometric quantities of diamine and dianhydrideare used to obtain the highest molecular weight, but the equivalentratio of dianhydride to diamine can range from 1:2 to 2:1.

Examples of suitable aromatic dianhydrides include:

1,2,5,6-naphthalene tetracarboxylic dianhydride;

1,4,5,8-naphthalene tetracarboxylic dianhydride;

2,3,6,7-naphthalene tetracarboxylic dianhydride;

2-(3′,4′-dicarboxyphenyl)5,6-dicarboxybenzimidazole dianhydride;

2-(3′,4′-dicarboxyphenyl)5,6-dicarboxybenzoxazole dianhydride;

2-(3′,4′-dicarboxyphenyl)5,6-dicarboxybenzothiazole dianhydride;

2,2′,3,3′-benzophenone tetracarboxylic dianhydride;

2,3,3′,4′-benzophenone tetracarboxylic dianhydride;

3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA);

2,2′,3,3′-biphenyl tetracarboxylic dianhydride;

2,3,3′,4′-biphenyl tetracarboxylic dianhydride;

3,3′,4,4′-biphenyl tetracarboxylic dianhydride(BPDA);

bicyclo-[2,2,2]-octen-(7)-2,3,5,6-tetracarboxylic-2,3,5,6-dianhydride;

thio-diphthalic anhydride;

bis(3,4-dicarboxyphenyl)sulfone dianhydride;

bis(3,4-dicarboxyphenyl)sulfoxide dianhydride;

bis(3,4-dicarboxyphenyl oxadiazole-1,3,4)paraphenylene dianhydride;

bis(3,4-dicarboxyphenyl)2,5-oxadiazole 1,3,4-dianhydride;

bis2,5-(3′,4′-dicarboxydiphenylether)1,3,4-oxadiazole dianhydride;

bis(3,4-dicarboxyphenyl)ether dianhydride or 4,4′-oxydiphthalicanhydride (ODPA);

bis(3,4-dicarboxyphenyl)thioether dianhydride;

bisphenol A dianhydride (BPADA);

bisphenol S dianhydride;

2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride or5,5-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]bis-1,3-isobenzofurandione)(6FDA);

hydroquinone bisether dianhydride;

bis(3,4-dicarboxyphenyl)methane dianhydride;

cyclopentadienyl tetracarboxylic acid dianhydride;

cyclopentane tetracarboxylic dianhydride;

ethylene tetracarboxylic acid dianhydride;

perylene 3,4,9,10-tetracarboxylic dianhydride;

pyromellitic dianhydride (PMDA);

tetrahydrofuran tetracarboxylic dianhydride; and

resorcinol dianhydride.

The dianhydrides can be used in their tetraacid form or as mono, di,tri, or tetra esters of the tetra acid, but the dianhydride form ispreferred because it is more reactive. The preferred dianhydride is ODPAbecause it has been found to give excellent properties. Mixtures ofdianhydrides are also contemplated. Additional amounts of monoanhydridesor tri- or higher functional anhydrides can be used to control molecularweight or crosslinking.

The diamine used in preparing the polyimide is preferably aromatic asaromatic diamines give the best properties. Examples of aromaticdiamines include:

m- and p-phenylenediamine;

2,4-diaminotoluene (TDA);

2,5- and 2,6-diaminotoluene;

p- and m-xylenediamine;

4,4′-diaminobiphenyl;

4,4′-diaminodiphenyl ether or 4,4′-oxydianiline; (ODA)

3,4′-oxydianiline;

4,4′-diaminobenzophenone;

3,3′,3,4′, or 4,4-diaminophenyl sulfone or m,m-, m,p- or p,p-sulfonedianiline;

4,4′-diaminodiphenyl sulfide;

3,3′-diaminodiphenyl sulfone (APS);

3,3′ or 4,4′-diaminodiphenylmethane or m,m- or p,p-methylene dianiline;

3,3′-dimethylbenzidine;

2,2′-bis[(4-aminophenyl)-1,4-diisopropyl]benzene or4,4′-isopropylidenedianiline or bisaniline P(BAP);

2,2′-bis[(4-aminophenyl)-1,3-diisopropyl]benzene or3,3′-isopropylidenedianiline or bisaniline M;

methylene dianiline;

1,4-bis(4-aminophenoxy)benzene;

1,3-bis(4-aminophenoxy)benzene;

1,3-bis(3-aminophenoxy)benzene (APB);

4,4′-bis(4-aminophenoxy)biphenyl;

2,4-diamino-5-chlorotoluene;

2,4-diamino-6-chlorotoluene;

2,2-bis-[4(4-aminophenoxy)phenyl]propane (BAPP);

trifluoromethyl-2,4-diaminobenzene;

trifluoromethyl-3,5-diaminobenzene;

2,2-bis(4-aminophenyl)-hexafluoropropane (6F diamine);

2,2-bis(4-phenoxy aniline)isopropylidene;

2,4,6-trimethyl-1,3-diaminobenzene;

4,4′-diamino-5,5′-trifluoromethyl diphenyloxide;

3,3′-diamino-5,5′-trifluoromethyl diphenyloxide;

4,4′-trifluoromethyl-2,2′-diamino biphenyl;

2,5-dimethyl-1,4-phenylenediamine (DPD);

2,4,6-trimethyl-1,3-diaminobenzene;

diaminoanthraquinone;

4,4′-oxybis[(2-trifluoromethyl)benzeneamine](1,2,4-OBABTF);

4,4′-oxybis[(3-trifluoromethyl)benzeneamine];

4,4′-thiobis[(2-trifluoromethyl)benzeneamine];

4,4′-thiobis[(3-trifluoromethyl)benzeneamine];

4,4′-sulfoxylbis[(2-trifluoromethyl)benzeneamine];

4,4′-sulfoxylbis[(3-trifluoromethyl)benzeneamine];

4,4′-ketobis[(2-trifluoromethyl)benzeneamine];

4,4′-[(2,2,2-trifluoromethyl-1-(trifluoromethyl)-ethylidine)bis(3-trifluoromethyl)benzeneamine];and

4,4′-dimethylsilylbis[(3-trifluoromethyl)benzeneamine].

The preferred aromatic diamine is APB as it gives excellent properties.Mixtures of aromatic diamines are also contemplated. Additional amountsof monoamines or tri- or higher functional amines can be used to controlmolecular weight or crosslinking.

The polyimide is preferably a polyimidesiloxane because apolyimidesiloxane has better solubility in the low-boiling solvents usedin this invention. To prepare a polyimidesiloxane, a diamine ordianhydride that contains siloxane groups is included as part of thediamine or the dianhydride. A polyimidesiloxane can be made from about 1to about 80 wt % siloxane-containing monomers and about 20 to about 99wt % monomers that do not contain siloxane. Preferably, it is made fromabout 20 to about 60 wt % siloxane-containing monomers and about 40 toabout 80 wt % monomers that do not contain siloxane. Thesiloxane-containing monomer can be either aromatic or non-aromatic, butnon-aromatic monomers are preferred as they are more readily available.Examples of siloxane diamines that can be used have the formula:

Examples of siloxane dianhydrides that can be used have the formula:

where R₁, R₂, and R₃ are mono, di, and triradicals, respectively, eachindependently selected from a substituted or unsubstituted 1 to 12carbon atom aliphatic group or a substituted or unsubstituted 6 to 10carbon atom aromatic group, where m is an average of 1 to 200. (Siloxanediamines are herein denoted by the notation “G_(m)”.) Preferably, m is 1to 12, R₁ is methyl, and R₂ is propyl as those compounds are morereadily available and work well. Examples of monoradicals include —CH₃,—CF₃, —CH═CH₂, —(CH₂)_(n)CF₃, —(CF₂)_(n)CF₃, —C₆H₅, —CF₃—CHF—CF₃, and

Examples of diradicals include —(CH₂)_(n)—, —(CH₂)_(n)—, —CF₂— and—C₆H₄—. Example of triradicals include ═CH—CH₂—,

Mixtures of siloxane monomers are also contemplated. Siloxane diaminesare preferred to siloxane dianhydrides as they are more readilyavailable. To increase solubility in the low-boiling solvent and enhancematerial properties, the diamine is preferably a mixture of about 5 toabout 55 wt % aromatic diamine that does not contain siloxane groups andabout 45 to about 95 wt % aliphatic diamine that contains siloxanegroups.

To prepare the polyimide, a slurry or solution in a low-boiling organicsolvent is formed of either the dianhydride monomer or the diaminemonomer, respectively. Because the dianhydride is usually less solublethan the diamine and it is more difficult to add the insolubledianhydride to a solution of the diamine, it is preferable to form aslurry of the dianhydride monomer and add to it a warmed-up solution ofthe diamine in some of the low-boiling. The diamine is preferably amixture of an aromatic diamine that does not contain siloxane groups andan aliphatic diamine that contains siloxane groups. A block copolymercan be formed by adding one of the two diamines to the slurry of thedianhydride before adding the other diamine.

The low-boiling solvent should have a boiling point between about 80 andabout 160° C. as higher boiling solvents are too difficult to remove andlower boiling solvents evaporate too readily from the adhesive; thepreferred boiling point of the solvent is about 120 to about 150° C. Theinvention is applicable to those solvents in which the polyamic acid isinsoluble at a temperature below the temperature at which it imidizes,i.e., typically about 140° C. Such solvents are usually less polar,i.e., have a dipole moment of less than about 3.5. Examples of suchsolvents include anisole, toluene, xylene, cyclohexanone,cyclopentanone, methyl ethyl ketone, methyl isobutyl ketone, benzene,hydrocarbons, and mixtures thereof. Anisole, toluene, xylene, methylethyl ketone, methyl isobutyl ketone, and mixtures thereof are preferredand anisole is especially preferred because it has a high conversion tothe imide, a low drying temperature, a low boiling point, and lowtoxicity. Toluene, benzene, and xylene form low-boiling azeotropes withthe water that is condensed out during imidization. It is thereforepreferable to add an azeotroping solvent with another low-boilingsolvent to form an azeotrope with the water of imidization that isformed and keep the temperature at which the water is removed bydistillation. The amount of azeotroping solvent should be sufficient toform an azeotrope with all of the water that is present; about 5 toabout 30 wt % of azeotroping solvent, based on total solvent, is usuallyadequate.

The solution or slurry of either diamine or dianhydride in the solventis heated to at least the temperature at which the polyamic acid fullyimidizes, typically about 80 to about 160° C., and preferably at reflux.At lower temperatures the polyamic acid may precipitate or fail to fullyimidize and at higher temperatures the method of this invention is notneeded as higher-boiling solvents, such as NMP, can be used. Thepreferred temperature range is about 120 to about 150° C. Highertemperatures with low-boiling solvents can be used if the solution orslurry is under pressure. Sufficient solvent should be used so that thefinal solution of the polyimide is about 1 to about 40 wt % solids. Lesssolids require processing too much solvent and higher solids are tooviscous. The solution of the polyimide is preferably about 25 to about35 wt % solids. The other monomer (i.e., dianhydride or diamine) is thenadded to the solution or slurry, preferably in a small amount of thesolvent. This addition is preferably at a rate that is slower than therate of imidization, typically over about an hour, to avoid clumping andto keep the temperature constant. The dianhydride and the diamine reactreadily to form a polyamic acid, which almost immediately is convertedinto a fully (i.e., over 95%) imidized polyimide.

The following examples further illustrate this invention:

EXAMPLE 1

To a 2 liter 3-necked flask equipped with a mechanical stirrer, athermometer, a reflux condenser and a Dean-Stark trap, 79.3 g (0.2557mole) of ODPA, 210 g of anisole, and 61 g of toluene were charged; thetemperature was raised to reflux. Into 248 g of anisole at 70° C. wasdissolved 37.4 g (0.1279 mole) of APB and 110.5 g G₉. Using a additionalfunnel, the solution was slowly added to the refluxing reactor over anhour. The water generated in the reaction was removed to the Dean-Stark.After the addition was complete, refluxing continued at about 135° C.for 3 hours; 205 g of anisole, toluene, and water were removed, giving aresin content was 39.9 wt %. The imidization was 98.8%. From gelpermeation chromatography (GPC) analysis, the Mw was 50,900 g/mole, theMn was 28,400 g/mole, and the polydispersity was 1.8

EXAMPLE 2—COMPARATIVE

To a 1 liter 3-necked flask equipped with a mechanical stirrer, athermometer, a reflux condenser and a Dean-Stark trap was added 350 ganisole, 63 g toluene, 37.23 g APB, and 108 g G₉. The slurry was warmedslightly to about 30° C. to completely dissolve the APB and 79.77 g ODPAwere added. The polymerization did not proceed at room temperature sothe reactor temperature was raised over 30 minutes to the refluxtemperature; the water was collected in a Dean-Stark trap. When thetemperature reached about 70° C., a precipitate of polyamic acidappeared in the solution. As the temperature was raised higher, a solid,white lump of polyamic acid formed which dissolved as imidizationproceeded. After three hours at reflux, 138 g of toluene, anisole, andwater were removed. The resin content of the solution was 34 wt %. Theimidization of the polyimidesiloxane was 97.4% and, from the GPCanalysis, Mw was 42,500, Mn was 26,500 g/mole, and the polydispersitywas 1.6.

EXAMPLE 3

To a 22 liter 3-necked flask equipped with a mechanical stirrer, athermometer, a reflux condenser and a Dean-Stark trap was added 871.97 gODPA, 2311 g anisole, and 676 g toluene. The temperature was raised toreflux and 410.7 g APB and 1188.4 g G₉ dissolved in 2725 g anisole at70° C. was mixed into the solution of APB over an hour. After theaddition was complete, the temperature was held at reflux for 3 hours;2,252 g of anisole, toluene, and water were removed; the resin contentwas 39.7 wt %. From GPC analysis, Mw was 50,900 g/mole, Mn 28,400g/mole, and polydispersity was 1.79.

EXAMPLE 4

To a 1 liter 3-necked flask equipped with a stirrer, an additionalfunnel, and a Dean-Stark trap with a reflux condenser under nitrogenpurge was added 79.7 g ODPA, 300 g anisole, and 73 g toluene; thetemperature was raised to reflux. To make a siloxane segment rich in themiddle of the polymer molecules, 108.5 g G₉ was added first over 30minutes. After the addition was complete, the reflux continued for 30minutes longer. Then 18.7 g APB and 54.2 g G₉ in 238 g anisole werewarmed to 70° C. to completely dissolve the APB. The solution of APB andG₉ was added to the refluxing solution over 30 minutes using anadditional funnel. After the addition was complete, the reaction wascontinued at reflux for 2½ hours to remove water, toluene, and anisole.The solids content was about 40 wt %, the imidization was 95%, and theresin content was 39.6%. From GPC analysis, the Mw was 50,000 g/mole,the Mn was 31,000, and the polydispersity was 1.6.

EXAMPLE 5

Example 4 was repeated using 79.7 g ODPA, 300 g anisole, and 73 gtoluene. To make the aromatic diamine rich in the middle of polymermolecules, a solution of 18.7 g APB and 54.2 g G₉ in 237 g anisolewarmed to 70° C. was added to the refluxing reactor over 30 minutes.Then 108 g G₉ was added over 30 minutes and the refluxing continued for2½ hours to distill off water, toluene, and anisole. The solids contentwas about 40 wt %, the imidization was 94.7%, and the resin content was38.4%. From GPC analysis, the Mw and Mw were 35,000 g/mole and 23,000g/mole, respectively, and the polydispersity was 1.53.

We claim:
 1. A solution comprising: at least one solvent that boils at a temperature between about 80° C. and about 160° C.; a diamine monomer; a dianhydride monomer, wherein the diamine monomer and dianhydride monomer react to form a polyamic acid; and a polyimide dissolved in the at least one solvent formed from the polyamic acid.
 2. The solution of claim 1, wherein the polyimide does not contain siloxane groups.
 3. The solution of claim 1, wherein the polyimide is a polyimidesiloxane.
 4. The solution of claim 3, wherein the polyimidesiloxane is made from about 20 to about 99 wt % of a monomer that does not contain siloxane groups and about 1 to about 80 wt % of a monomer that contains siloxane groups.
 5. The solution of claim 4, wherein the dianhydride monomer is aromatic and does not contain siloxane groups.
 6. The solution of claim 5, wherein said diamine monomer is a mixture of about 5 to about 55 wt % of an aromatic diamine that does not contain siloxane groups and about 45 to about 95 wt % of an aliphatic diamine that contains siloxane groups.
 7. The solution of claim 6, wherein said aromatic diamine is 1,3-bis(3-aminophenoxy)benzene.
 8. The solution of claim 6, wherein the siloxane containing diamine has the general formula:

where R₁ and R₂ are mono and diradicals, respectively, each independently selected from a substituted or unsubstituted 1 to 12 carbon atom aliphatic group or a substituted or unsubstituted 6 to 10 carbon atom aromatic group, and m is an average of 1 to
 200. 9. The solution of claim 1, wherein the at least one solvent is a mixture of two solvents, one of which forms a low-boiling point azeotrope with water.
 10. The solution of claim 9, wherein the at least one solvent is selected from the group consisting of anisole, toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, and mixtures thereof.
 11. The solution of claim 10, wherein the at least one solvent is anisole.
 12. The solution of claim 1, wherein the dianhydride monomer is bis(3,4-dicarboxyphenyl)ether dianhydride.
 13. The solution of claim 1, wherein the polyamic acid substantially does not precipitate.
 14. The solution of claim 1, wherein the polyamic acid is imidized before the polyamic acid precipitates.
 15. The solution of claim 14, wherein the polyamic acid is insoluble in said solution.
 16. The solution of claim 1, wherein the polyamic acid is insoluble in the at least one solvent at a temperature below where the polyamic acid is imidized.
 17. The solution of claim 1, wherein the dianhydride is aromatic, wherein the at least one solvent is selected from the group consisting of anisole, toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, and mixtures thereof, and wherein the diamine monomer includes: an aromatic diamine that does not contain siloxane groups in an amount of about 5 to 55 wt % based on total diamine monomer weight, and an aliphatic diamine that contains siloxane groups in an amount of about 45 to 95 wt % based on total diamine monomer weight.
 18. The solution of claim 17, wherein the at least one solvent is a mixture of anisole and another solvent selected from the group consisting of toluene, xylene, and benzene.
 19. The solution of claim 1, wherein the dianhydride monomer is a bis(3,4-dicarboxyphenyl)ether dianhydride, wherein the at least one solvent includes anisole and sufficient amount of a solvent selected from the group consisting of toluene, xylene, and benzene to azeotrope water, wherein the diamine monomer includes: a 1,3-bis(3-aminophenoxy)benzene in an amount of about 40 to about 80 wt % based on total diamine monomer weight, and an aliphatic diamine in an amount of about 20 to about 60 wt % based on total diamine monomer weight having the general formula:

where R₁ is methyl, R₂ is propyl, and m is an average of 1 to
 12. 